In electrophotography methods, an electric latent image is formed on an image carrier, the latent image is developed with a toner, the resulting toner image is transferred onto a print material such as paper, and the image is fixed by heat, pressure, etc. Only a black toner may be used in conventional manner to form an image, and toners for different colors may be used to form a full color image.
The toners may be used as a 2-component developing agent mixing with carrier particles, or as a 1-component developing agent of a magnetic or nonmagnetic toner. The toners are generally produced by kneading pulverization methods. In the kneading pulverization methods, a binder resin, a pigment, a releasing agent such as a wax, a charge controlling agent, etc. are melt-kneaded, cooled, finely pulverized, and classified to produce desired toner particles. Inorganic and/or organic fine particles are attached to the surfaces of the toner particles produced by the kneading pulverization method in accordance with the intended use, thereby producing the toners.
In the case of using the kneading pulverization methods, it is difficult to purposefully control the shape of the toner particles. Further, particularly when a highly pulverizable material is used, the toner particles tend to be excessively micronized. Thus, in the 2-component developing agents, the micronized toner particles may be bonded to carrier surfaces to accelerate charge deterioration of the developing agents, and in the 1-component developing agents, the micronized toner particles may be scattered and the development property may be lowered due to the toner shape change to deteriorate image qualities. Furthermore, when the toner is pulverized at a boundary between a binder resin and wax, the wax is easily eliminated from the toner, so that developing rollers, image carriers, carriers, etc. are contaminated to reduce reliability of the developing agent.
Under such circumstances, emulsion polymerization aggregation methods have recently been proposed as methods of purposefully controlling shape and surface composition of toner particles in JP-A-63-282752 and JP-A-6-250439.
In the emulsion polymerization aggregation methods, a resin dispersion liquid is prepared by emulsion polymerization, a colorant dispersion liquid is prepared by dispersing a colorant in a solvent, the dispersion liquids are mixed to form aggregated particles with diameters appropriate for toner particles, and the aggregated particles are fused by heating to obtain toner particles. The shape of the toner particles can be controlled to be amorphous or spherical by changing the heating temperature in the emulsion polymerization aggregation methods.
In the emulsion polymerization aggregation methods, at least the fine resin particle dispersion liquid and the colorant dispersion liquid are aggregated and fused under predetermined conditions to obtain a toner. However, only limited resins can be synthesized in the emulsion polymerization aggregation methods. The methods cannot be used for producing polyester resins known as excellent in fixity though they are suitable for producing acrylic styrene copolymers.
Though phase inversion emulsification methods, which contain dissolving a polyester resin in an organic solvent, adding a pigment dispersion liquid, etc. thereto, and then adding water, are known as methods for producing toners using polyester resins, the methods require the processes of removing and recovering the organic solvent. A method for producing fine particles by mechanical shearing in an aqueous medium without using organic solvents is proposed in JP-A-9-311502, and however a resin melt, etc., hard to handle, has to be supplied to a stirring apparatus in the method. Further, the method is poor in freedom of shape control, and the toner shape cannot be freely controlled to be amorphous, spherical, etc.